Gulf of Maine Seasonal Sea Surface Temperature Update
Seasonal Patterns in Sea Surface Temperatures
About the Updates:
Over the past decade, scientists at the Gulf of Maine Research Institute have led a body of research that highlights the rapid pace of warming in the Gulf of Maine. To keep you informed, we share seasonal updates about conditions in the Gulf of Maine.
New in 2023: Moving the Climatological Reference Period
In the field of climate science, 30-year time periods are a standard measure for a “climatological reference period”. Such a timescale adequately captures the natural inter-annual variability of the Earth system to enable rigorous statistical analysis of trends in environmental conditions. This is particularly relevant when presenting statistics such as temperature “anomalies”—or deviations from these 30-year climatological averages. To date, when we present temperature anomaly data in our seasonal and annual warming updates, we have used a climatological reference period of 1982-2011. In part, this is motivated by the fact that reliable satellite data for sea surface temperatures (SST) in the Gulf of Maine became available in 1982 (and 30 years hence brought us to 2011). Beginning with this winter 2022-23 Gulf of Maine warming report, we are using a new 30-year climatological reference period, 1991-2020, reflecting the fact that an additional decade’s worth of data has been collected, enabling us to update our baseline reference period. This change is consistent with best practices used by the international science community. For more information on 30-year climatological (or baseline) reference periods, the motivation for, and implications of updating it to 1991-2020, visit the U.S. “Climate Normals” database or this explainer from the National Oceanic and Atmospheric Administration (NOAA).
For the Gulf of Maine, the update of the seasonal climatology can be seen most clearly in February and March as temperatures no longer reach peak-lows. As well as in August and September where temperatures are setting new records. SST is higher throughout the year with this new climatology, and this will be reflected in all figures and tables as anomalies from this CRP will be lowered. However, underlying trends will remain unchanged, as will warming rates.
Learn more about how scientists study climate, and the details of this transition, in our marine heatwaves technical report.
Note About the Data: The figures in this report are created using remotely-sensed satellite data as part of publicly funded research efforts. Satellite SST data was obtained from NOAA’s National Center for Environmental Information (NCEI), with all maps and figures displaying NOAA’s Optimum Interpolation Sea Surface Temperature Data.
The Gulf of Maine Region
For analyses like these, it is important to be clear about the spatial extent that “defines” the Gulf of Maine (Figure 1), as different borders could produce different results. The spatial domain we use as the “Gulf of Maine” is displayed below. This area is consistent with previous seasonal and annual Gulf of Mainereports GMRI has produced.
Season Highlights
For this seasonal report we present an analysis of SST for winter 2022-23 (December 1st - February 28th). During this season, the average SST for the Gulf of Maine was 47.64°F, making it the new hottest winter on record for the period of 1982-2023 — the period over which the satellite data used are available.
Weekly Temperatures
In (Table 1), we highlight how the SST for each week this winter compares to the 30-year CRP period (i.e., climatological averages from 1991 through 2020) for the area shown in Figure 1.
The observed SST, long-term average SST trends, and SST anomalies (i.e., departures from the long-term average SST) are shown. Departures from the long-term average hovered around 3°F above normal with a few weeks punctuated by anomalies in excess of 4F in early- to mid-December and from late January through most of February with the last of 2022 and first week of 2023 experiencing temperatures closest to the long-term average.
| Weekly Sea Surface Temperatures - Winter | ||||||
| (December 1, 2022 - February 28th, 2023) | ||||||
| One-Week Period | Observed Temperature | Climatological Average | Temperature Anomaly | |||
|---|---|---|---|---|---|---|
| °F | °C | °F | °C | °F | °C | |
| Dec 01 - Dec 03 | 52.40 | 11.40 | 49.30 | 9.64 | 3.10 | 1.72 |
| Dec 04 - Dec 10 | 53.00 | 11.70 | 48.70 | 9.25 | 4.33 | 2.41 |
| Dec 11 - Dec 17 | 52.50 | 11.40 | 47.70 | 8.72 | 4.83 | 2.68 |
| Dec 18 - Dec 24 | 50.60 | 10.30 | 46.70 | 8.19 | 3.88 | 2.15 |
| Dec 25 - Dec 31 | 47.80 | 8.77 | 45.80 | 7.68 | 1.96 | 1.09 |
| Jan 01 - Jan 07 | 46.40 | 7.99 | 44.90 | 7.18 | 1.45 | 0.81 |
| Jan 08 - Jan 14 | 46.50 | 8.04 | 44.10 | 6.71 | 2.40 | 1.34 |
| Jan 15 - Jan 21 | 46.60 | 8.10 | 43.30 | 6.25 | 3.33 | 1.85 |
| Jan 22 - Jan 28 | 46.70 | 8.14 | 42.50 | 5.85 | 4.13 | 2.29 |
| Jan 29 - Feb 04 | 46.10 | 7.86 | 41.90 | 5.48 | 4.28 | 2.38 |
| Feb 05 - Feb 11 | 44.70 | 7.05 | 41.30 | 5.16 | 3.40 | 1.89 |
| Feb 12 - Feb 18 | 45.20 | 7.31 | 40.80 | 4.90 | 4.34 | 2.41 |
| Feb 19 - Feb 25 | 45.20 | 7.34 | 40.40 | 4.68 | 4.78 | 2.65 |
| Feb 26 - Feb 28 | 43.80 | 6.58 | 40.20 | 4.57 | 3.63 | 2.02 |
| Data Source: NOAA OISSTv2 Daily Sea Surface Temperature Data. | ||||||
| Climatological Reference Period: 1991-2020. | ||||||
Monthly Statistics
Table 2 shows monthly average SST for winter 2022-23, where we see each month was nearly 3°F or more above the 1991-2020 CRP. February showed the largest deviation from the long-term climatological average, with an average SST anomaly of 4.11°F.
| Month | Monthly SST Ranking | Observed Temperature | Climatological Average | Temperature Anomaly | Temperature Progression | |||
|---|---|---|---|---|---|---|---|---|
| °F | °C | °F | °C | °F | °C | High/Low °F | ||
| Dec | 1 | 51.10 | 10.60 | 47.40 | 8.57 | 3.69 | 2.05 | |
| Jan | 3 | 46.50 | 8.07 | 43.50 | 6.41 | 2.99 | 1.66 | |
| Feb | 1 | 45.00 | 7.23 | 40.90 | 4.95 | 4.11 | 2.28 | |
| Data Source: NOAA OISSTv2 Daily Sea Surface Temperature Data. | ||||||||
| Climatological Reference Period: 1991-2020. | ||||||||
Seasonal Trends and Anomalies in Context
The Gulf of Maine is an area of particular interest to the scientific community because of the remarkable rate of warming it has experienced in recent years coupled with its importance as a major driver for the regional economy.
When looking at average winter temperatures from the beginning of the satellite record in 1982 Figure 2, there is a clear long-term increase, with SST’s warming at a rate of 0.81°F per decade. This rate of seasonal wintertime warming is ~4x the rate that global ocean temperatures are warming (0.21°F per decade).
The unprecedented levels of warmth over the past decade or so are consistent with what researchers believe has been a distinct regime shift in terms of the major influences on SSTs in the Gulf of Maine. The drivers of this (e.g., a potential weakening of the Atlantic Meridional Overturning Circulation, widening of the Gulf Stream, changes in the characteristics of the Labrador Current) have been well-documented in the peer-reviewed literature, including through research by GMRI scientists.
How Does this Winter Compare?
2023 2022-23 is the new warmest winter season observed in the Gulf of Maine during the 41 years we have satellite data to analyze. The top 5 warmest winter seasons have all occurred in the last decade.
Marine Heatwave Conditions
The most commonly used definition of a “marine heatwave” (MHW) is when daily average SSTs exceeded the 90th percentile of a climatological (i.e., 30-year) average for at least 5 consecutive days. Gaps of 2 days or less in this threshold do not constitute a break in the MHW event.
Using this broadly accepted definition, the Gulf of Maine has experienced MHW conditions for 82% of this winter. A 16 day period over the New-Year’s transition (Dec 27th - January 11th) were the only dates where SST was below the threshold of a MHW.
Presenting SST conditions in terms of anomalies (Figure 5) as opposed to absolute values (Figure 4) illustrates in greater detail the magnitude of MHW conditions throughout the winter. The most extreme daily SST anomalies occurred in December, with temperatures exceeding 5°F above the climatological average. Temperatures fell closer to the CRP average towards the end of December, before rising to the +3 to +4°F range for the second half of January and through February.
Heatmap of Temperature Anomalies and Heatwave Events
Looking at the full record of daily SST anomalies in the Gulf of Maine (Figure 6), the distinct thermal regime shift beginning around 2010 is evident. Indeed, since 2012, the Gulf of Maine has experienced far more persistent MHW conditions (indicated by solid black lines) than at any other point in the satellite record.
The Visual Impact of a New Climate Reference Period
If we compare our new heatmap figure (Figure 6) to what it was previously, the transition to a new climatological reference period can be seen more clearly. Using the slider below, we can reveal that the transition has removed many of the heatwave events prior to 2012. The new CRP has also impacted how severe the thermal stress of the last decade appears. This period is still clearly distinct in terms of higher temperatures and the frequency of MHW events, but the MHW record has been changed.
Spatial Distribution of Seasonal Anomalies
From a spatial perspective, the Gulf of Maine and (most) surrounding areas experienced above average SSTs during winter 2022-23, but the warmest patches were to the south and east of Georges Bank, mostly outside the domain analyzed in preceding sections. The highest seasonally averaged anomaly of any location above was 11.41°F.
Monthly Temperature Anomalies
Average monthly SST anomalies are shown in Figure 10. The warmest anomalies were observed in December and February and were largely confined to areas just beyond the region of study (i.e, beyond the continental shelf where the Gulf Stream and Labrador Current have significantly more influence on oceanic conditions).
A Note on Data Sources:
NOAA_ERSST_V5 data provided by the NOAA/OAR/ESRL PSL, Boulder, Colorado, USA, from their Web site at https://psl.noaa.gov/data/gridded/data.noaa.ersst.v5.html.
NOAA High Resolution SST data provided by the NOAA/OAR/ESRL PSL, Boulder, Colorado, USA, from their Web site at https://psl.noaa.gov/data/gridded/data.noaa.oisst.v2.highres.html.
Citing This Work
If you would like to cite this report, please use:
Gulf of Maine Research Institute. 2022. Gulf of Maine Warming Update: Winter 2023